I have a 3 yr old. Started coughing 2 nights ago not constant sounds kinda phlyemy and no other symptoms. Very low grade fever at night. Contagious?

Possibly. If there is a fever over 101f, she may be contagious. Give lots of fluids, run a cool mist humidifier, and use Acetaminophen for fever or pain. If fever and cough persists for more than a few days, or symptoms are getting worse, she should be seen by her doctor.